Process for synthesis of telechelic urethane acrylate UV curable pre-polymeric materials

ABSTRACT

The present invention involves the design of a radiation curable organic pre polymer resin material based on urethane acrylic linkage synthesized from the natural renewable resource cardanol or a derivative thereof, for coating application. These new molecules have a faster and better curing rate compared to the starting renewable resource—cardanol. This is brought about by the hydrogen bonding of the urethane linkage which leads to a pre organization of the molecules in such a way as to bring the cross linkable double bonds closer to each other. The present invention also involves a UV curable formulation of the above mentioned resins along with 2-10 parts by weight of a photopolymerization initiator. The resin, either in a formulation or alone turns into a cross linked film upon photopolymerization in presence of photoinitiator under a UV curable radiation source like a mercury vapor pressure lamp.

This Application is a National Phase Application of InternationalApplication No. PCT/IN2005/000454 filed Dec. 30, 2005.

FIELD OF INVENTION

The present invention relates to the design and synthesis of a UVradiation curable organic pre polymer based on urethane acrylic linkagesynthesized from the natural renewable resources like cardanol or aderivative thereof.

BACKGROUND OF THE INVENTION

Cashew nut shell liquid (CNSL), which is a by product of the cashewindustry, plays a significant role in the search for cost effectivematerials which are also renewable. Double distillation of CNSL yieldscardanol—a phenol, having a C15 side chain that contributes flexibility,chemical resistance and adhesion in materials prepared from it. Due tothis versatile nature, it finds applications in many areas like surfacecoatings, epoxy, varnishes, paints, printing inks, phenolic resins,rubber compounding, lacquers, laminates, friction materials, andadhesives. In general, CNSL and cardanol are used as phenolic resins bycondensation with active hydrogen containing compounds likeformaldehyde. In addition, the unsaturation in the C15 side chain makesit amenable to free radical polymerization in presence of commonlyavailable thermal initiators and also to UV initiated polymerization inpresence of suitable photoinitiators. However, the double bonds in thelong alkyl side chain are not as reactive compared to an acrylic ormethacrylic double bond. Functionalization of cardanol with acrylate ormethacrylate moiety gives rise to cross linked polymers as reported inthe U.S. Pat. No. 6,765,079 by Saminathan, M. et. al. However, cardanylacrylate and methacrylate based crosslinkers are usually not very stableand often result in the formation of gels. Moreover, photopolymerizationleads to shrinkage and the resultant stress causes defects in the bondline and in the resin matrix in the case of fully UV cured(meth)acrylate systems. Compared to free radical cured acrylate resins,polyurethane systems do not show shrinkage related stress. Dual curecoatings involving urethane acrylates combine the benefits of UV curingwith that of a two component urethane system and overcome some of theirlimitations. The cured films are usually more flexible and adhere betterto the substrate than 100% UV curable systems, probably becauseshrinkage is reduced. Acrylic resins with urethane side groups arecapable of hydrogen bonding and they exhibit very fast polymerizationrates as shown in Macromolecules, 36, (2003) 3861 by Jansen, J. F. G. Aet al. Thus acrylic resins with urethane linkage have the addedadvantage of hydrogen bonding which leads to organization of the monomerunits, which in turn increases the rate of polymerization, asillustrated in Eur. Polym. J. 41, (2004), 23 by Asha, S. K. et al.Although reports concerning polyurethanes based on cardanol formaldehyderesin are known, there are not many reports on urethanes synthesizeddirectly from cardanol. Bhunia, H. P. et al. have reported thefunctionalization of cardanol to obtain a diazo monomer which uponfurther reaction with diisocyanates gave rise to polyurethane in the J.Polym. Sci: Part A: Polym Chem, 36 (1998) 391. The synthesis ofpolyurethanes using hydroxy alkylated cardanol formaldehyde as well ascardanol-lignin-formaldehyde resins are reported and the introduction ofthe urethane functionality has been shown to improve the thermalstability and mechanical properties of the final material as evidencedin the following references. Tan, T. T. M. Polym. International, 41(1996) 13; Sathiyalekshmi, V et. al Adv. Polym. Tech. 23 (2004) 91. Somepatents reported on the development of polymeric materials based onphenolic resin mixed with polyisocyanates and additives are also givenin Japanese patent publications (1). Akio, I.; Shigetoshu, A.; Isao, K.;Kkazuuo, T. 62-241914, 1987. (2). Noriimasa, Y.; Noratake, S. 63-97641,1988. (3). Tsutomu, N.; Koichi, K.; Yoshi, M.; Yuki. 63-213512, 1988.(4). Hisamitsu, I.; Yukio, S. 63-264616, 1988. (5). Laitar; Robert U.S.Pat. No. 4,698,377, 1987.

Thus, cardanol is known to have various potential industrial uses suchas resins, surface coatings etc, and development of new applications orimprovement of properties of materials based on cardanol by way of newmolecular design is strongly desired. Therefore, it is advantageous tohave coating compositions containing pre polymers based on cardanol,which combines the added advantage of having a urethane acrylic linkageincorporated in them. In the light of the foregoing discussion, theapplicant proposes a UV curable telechelic urethane acrylic pre polymer,based on cardanol or derivative of cardanol.

OBJECTS OF THE INVENTION

It is therefore the main object of the invention to provide a processfor the synthesis of telechelic urethane acrylate UV curable pre polymermaterials from the natural material cardanol as well as its derivatives.

It is another object of the invention to provide a process for thecuring of the pre polymer macromolecules in the presence of 2-10 partsby weight of photoinitiators under a source of UV irradiation.

Yet another object of the present invention is to make use of secondaryinteractions like the hydrogen bonding of urethane linkages to improvethe curing rate.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for the synthesisof a resin based on telechelic urethane acrylate UV curable pre-polymermaterials from renewable resources like cashew nut shell liquid (CNSL)for coating purposes, the process comprising the steps of

-   (a) coupling of one equivalent of the diisocyanate molecule    represented by structure I with one equivalent of the hydroxy    methacrylate molecule represented by structure II in order to obtain    the molecule represented by structure III,-   (b) coupling of one equivalent of molecule represented by structure    III with one equivalent of cardanol or its derivatives obtained from    renewable resources represented by structure IV in the presence of    organo metallic catalysts to obtain the final telechelic urethane    acrylate UV curable pre polymer resin material represented by    formula V,-   (c) curing of the telechelic urethane acrylate resin represented by    the formula V in presence of 2-10 wt % of a photoinitiator under a    UV curing source of radiation having wavelength 90-600 nm, and-   (d) formulating the above said resins with mono and multifunctional    acrylic oligomers so as to get a resin formulation for coating on    substrates.

The present invention also provides a process for the synthesis of aresin based on telechelic urethane acrylate UV curable pre polymermaterials from renewable resources like cashew nut shell liquid (CNSL)for coating purposes, the process comprising the steps of

-   (a) coupling of one equivalent of the diisocyanate molecule    represented by structure I, in the scheme-2 below with one    equivalent of cardanol or its derivatives obtained from renewable    resources represented by structure IV in order to obtain the    molecule represented by structure III″,-   (b) coupling of one equivalent of molecule represented by structure    III″ with one equivalent of hydroxy methacrylate molecule    represented by structure II in the presence of organo metallic    catalysts to obtain the final telechelic urethane acrylate UV    curable pre polymer resin material represented by formula V,-   (c) curing of the telechelic urethane acrylate resin represented by    the formula V in presence of 2-10 wt % of a photoinitiator under a    UV curing source of radiation having wavelength 90-600 nm, and-   (d) formulating the above said resins with mono and multifunctional    acrylic oligomers so as to get a resin formulation for coating on    substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

The other features and advantages of the invention will become apparentfrom the description and the accompanying drawing in which,

FIG. 1 represents the ¹H-NMR spectra of the telechelic urethanemethacrylate of cardanol, Isophorone diisocyanate (IPDI) andhydroxyethyl methacrylate (HEMA) in CDCl₃. The different types of theprotons in the structure are assigned by alphabets.

FIG. 2 represents the FTIR spectra of Cardanol (a) before (dotted line)and (b) after 60 min UV irradiation in the presence of a photoinitiatorusing a home-made UV cure setup.

FIG. 3 represents the FTIR spectra of telechelic urethane methacrylateof cardanol-IPDI-HEMA (a) before (dotted line) and (b) after 60 min UVirradiation in the presence of a photoinitiator using a home-made UVcure setup.

FIG. 4 represents the FTIR spectra of telechelic urethane methacrylateof Modified cardanol-HMDI-HEMA (a) before (dotted line) and (b) after 60min UV irradiation in the presence of a photoinitiator using a home-madeUV cure setup.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will now be explainedwith reference to the accompanying drawings. It should be understoodhowever that the disclosed embodiment is merely exemplary of theinvention, which may be embodied in various forms. The followingdescription and drawings are not to be construed as limiting theinvention and the numerous specific details are described to provide athrough understanding of the present invention, as the basis for theclaims and as a basis for teaching one skilled in the art how to makeand/or use the invention. However in certain instances, well-known orconventional details are not described in order not to unnecessarilyobscure the present invention in detail.

The present invention essentially comprises of the synthesis oftelechelic urethane acrylates (V) of cardanol as well as derivatives ofcardanol as UV curable resins capable of enhanced curing rate broughtabout by the hydrogen bonding units inbuilt in their molecular design.Urethane acrylates based on both cardanol and derivatives of cardanolwas synthesized as shown in scheme 1. The urethane methacrylate isproduced from the reaction of a polyisocyanate with cardanol orderivatives of cardanol (represented by formula IV in scheme 1), andanother compound containing at least one active hydrogen atom and atleast one (meth)acryloyloxy group. These compounds are obtained byreacting one mole of an aromatic, aliphatic or cycloaliphaticdiisocyanate represented by formula I with one mole of cardanol orderivatives of cardanol (IV), followed by coupling with one mole of acompound containing at least one active hydrogen atom and represented bythe general structure II. The order of coupling could also be couplingof one equivalent of the compound having both active hydrogen as well as(meth)acryloyloxy group represented by formula II with one equivalent ofthe diisocyanate represented by formula I followed by coupling with oneequivalent of the natural resource based compound represented by formulaIV. FIG. 1 shows the structural characterization of telechelic urethanemethacrylate of cardanol based on isophorone diisocyanate. The fouraromatic protons of cardanol appear at 7.12 and 6.68 ppm, whereas theunsaturation in the side chain (‘h’) appears at 5.37 ppm respectively.The sharp, well separated peaks (labeled ‘a’) at 6.15 and 5.43 ppmcorresponds to the methacrylic double bond protons, the peaks at 4.33(‘c, d’) corresponds to the ethylene oxide protons (—OCH₂CH₂OCO—) of thehydroxy ethyl methacrylate part. Similarly, the other telechelicurethane methacrylates of cardanol as well as derivatives of cardanolwere characterized using NMR spectroscopy.

The above described UV curable pre polymers could be used singly. It ishowever, preferred to use these in combination with compounds containingtwo or more (meth)acryloyloxy groups, which are useful as componentscapable of imparting better properties to the final coating and 2-10parts by weight of photoinitiators in the presence of a UV curingsource. The UV curable source could be low, medium or high pressuremercury lamp or xenon lamp having wavelength in the range 90-600 nm. Thephotoinitiators could be aromatic carbonyl compounds such as benzil,benzil dimethyl ketal, acetophenone, substituted acetophenones,thioxanthone or chlorothioxanthone in the range of 2-10 wt %. By varyingthe ratios of the various oligomers as well as optimizing the amount ofphotoinitiator used, the final film property of the cross linkedmaterial can be controlled. The above defined UV curable resinformulation could become a promising candidate in the coating oradhesive industry.

Cardanol as well as derivatives of cardanol has unsaturation in the sidechain which can be cured using standard photoinitiators, under UVirradiation. However, irradiation of both cardanol and modified cardanolin presence of the photoinitiator under the same laboratory conditionsinside a home-made UV curing setup showed that cardanol remained as aliquid without much curing happening, whereas the modified cardanolappeared like a transparent film; though still tacky, in a very shorttime. The curing kinetics could be followed by the disappearance of thepeaks of unsaturation using an FTIR spectrometer. In cardanol the peakintensity did not vary much (FIG. 2), whereas in the telechelic urethanemethacrylates of cardanol as well as derivatives of cardanol, theintensity of the above mentioned unsaturation peaks reduced drastically.Cardanol and its derivatives are known for their anti-oxidant propertiesas discussed in J. Chem. Soc. Perkin Trans, 2 (2001) 2142-2146 byAmorati, R.; et al., which explains the difficulty in its photoinducedcuring process. In the urethane (meth)acrylate pre polymers (V), inaddition to the unsaturation in the side chain, there is a polymerizable(meth)acryloyloxy group which also can undergo curing in presence ofphotoinitiators. Complete disappearance of the methacrylic double bondas observed in their FTIR spectra leads to the formation of atransparent film of the cross linked material. FIGS. 3-4 gives the FTIRspectra of the telechelic urethane methacrylates of cardanol as well asderivatives of cardanol with the peak positions labeled.

According to the present invention the UV curable telechelic urethanemethacrylic resin are synthesized from the renewable resource cardanolas well as the derivatives of cardanol.

According to another aspect of the present invention UV curing of theabove mentioned resins were carried out in the presence of an addedphotoinitiator, under a UV source from a home made UV cure setup.

The novel UV curable resins are directly prepared from renewableresource material cardanol. The present process combines the highlyversatile polyurethane chemistry with the natural abundance of renewableresources.

UV curing technology is so well advanced now that there is a whole hostof applications based on them, which we come across in our day to daylife; for example wood finishings, floorings, dental adhesives, CD's,DVD's, printing ink etc. Economic concerns are the main driving forcebehind the adoption of UV curing technology. Increased production speedcan lead to increase in sales, reduction in cost etc. Any moleculardesign strategy for the resin that can increase the curing rate willdefinitely lead to improved economy. Thus, the molecular designenvisaged in this invention brings about faster cure rate compared tothe parent resin, by virtue of hydrogen bonding which brings about a preorganization of the molecules whereby the (meth)/acrylic double bondsare brought closer to each other. The raw materials for the UV-curableresins are mostly based on petroleum based products, most of which areimported and are very expensive. The renewable resource based resins isvery attractive compared to the petroleum-based ones because of largeavailability, low cost and ease of scale-up for industrial applications.The molecular design envisaged in this invention, incorporates hydrogenbonding urethane methacrylate units into the cardanol moiety, which hasthe added advantage that it incorporates weather resistant methacrylicunits into the otherwise totally aromatic system.

The invention is described in detail in the following examples, whichare given by way of illustration only and therefore should not beconstrued to limit the scope of the present invention.

EXAMPLE 1 Synthesis of Cardanol-IPDI-HEMA

Isophorone diisocyanate [IPDI] (0.73 g, 0.003 moles) in 10 ml dry DMFwas taken in a 100 ml two necked flask. 2-Hydroxy ethyl methacrylate[HEMA][0.43 g, 0.003 moles] was added drop wise with constant stirringunder nitrogen. The reaction mixture was allowed to proceed under roomtemperature for 1 and a half hours. Then 3 drops of dibutyl tindilaurate [DBTDL] was added as catalyst followed by drop wise additionof cardanol (1 g, 0.0033 moles) in 10 ml DMF. It was left stirring atroom temperature for further 2 hours. It was then heated to 55° C. andmaintained at that temperature for 2 hours. Then, the contents werepoured to 150 ml water and extracted with dichloromethane. It was thenwashed with plenty of water and dried in vacuum oven at 60° C. for 12hours. Yield=90% (1.95 g)

EXAMPLE 2 Synthesis of Cardanol-IPDI-HEMA by Alternate Method

Isophorone diisocyanate [IPDI] (0.73 g, 0.003 moles) in 10 ml dry DMFwas taken in a 100 ml two necked flask. Cardanol (1 g, 0.0033 moles) in10 ml DMF was added drop wise with constant stirring under nitrogen. Thereaction mixture was allowed to proceed under room temperature for 1 anda half hours. Then 3 drops of dibutyl tin dilaurate [DBTDL] was added ascatalyst followed by drop wise addition of 2-Hydroxy ethyl methacrylate[HEMA][0.43 g, 0.003 moles]. It was left stirring at room temperaturefor further 2 hours. It was then heated to 55° C. and maintained at thattemperature for 2 hours. Then, the contents were poured to 150 ml waterand extracted with dichloromethane. It was then washed with plenty ofwater and dried in vacuum oven at 60° C. for 12 hours. Yield=90% (1.95g)

EXAMPLE 3 Synthesis of Modified Cardanol-HMDI-HEMA

Cardanol was modified by coupling it with 2-chloroethanol in presence ofK₂CO₃ and KI in DMF under inert atmosphere. Hexamethylene diisocyanate[HMDI] (0.49 g, 0.003 moles) in 10 ml dry DMF was taken in a 100 ml twonecked flask and the contents were cooled with ice. HEMA (0.38 g, 0.003moles) was added drop wise with constant stirring under nitrogen. Thereaction was allowed to proceed under ice cold condition for 2 hr. Thenthe reaction was kept at room temperature for 1 hr. After that thereaction was changed to ice cold condition and 3 drops of DBTDL wasadded as catalyst followed by drop wise addition of modified cardanol (1g, 0.003 moles) in 10 ml DMF. It was left stirring under cold conditionfor a further 1 hr and allowed to attain room temperature. Then thereaction was heated to 50° C. for 12 hrs. The contents were poured to150 ml water and extracted with dichloromethane. It was then washed withplenty of water and dried in vacuum oven at 60° C. for 12 hrs. Yield=62%(1.17 g). The same synthetic procedure is adopted for all types ofvariation in the diisocyanate chemistry or in the hydroxy(meth)acryloxychemistry or natural resource with active hydrogen atom to obtain thefinal UV curable telechelic pre polymer with varying R1, R2, R3, R4, R5and R6.

Although the invention has been described with reference to the specificembodiment, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternate embodiments of the invention will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that such modifications can be made withoutdeparting from the spirit and scope of the present invention as definedin the appended claims.

1. A process for the synthesis of a telechelic urethane acrylate UVcurable prepolymer material comprising: (a) coupling one equivalent ofthe diisocyanate molecule represented by structure I, in the scheme-1below with one equivalent of the hydroxy methacrylate moleculerepresented by structure II in order to obtain the molecule representedby structure III, (b) coupling of one equivalent of molecule representedby structure III with one equivalent of cardanol or a derivative thereofobtained from a renewable resources and represented by structure IV, inthe presence of an organo metallic catalyst to obtain the finaltelechelic urethane acrylate UV curable pre polymer resin materialrepresented by formula V:


2. A process for the synthesis of a telechelic urethane acrylate UVcurable prepolymer material comprising the steps of: (a) coupling of oneequivalent of the diisocyanate molecule represented by structure I, inthe scheme-2 below with one equivalent of cardanol or its derivativesobtained from renewable resources represented by structure IV in orderto obtain the molecule represented by structure III, (b) coupling of oneequivalent of molecule represented by structure III″ with one equivalentof hydroxy methacrylate molecule represented by structure II in thepresence of organo metallic catalysts to obtain the final telechelicurethane acrylate UV curable pre polymer resin material represented byformula V:


3. The process of claim 1 or 2 wherein the telechelic urethane acrylatematerial of formula V is cured in presence of 2-10 wt % of aphotoinitiator under a UV curing source of radiation having wavelength90-600 nm, and then formulated with mono and/or multifunctionaloligomers to obtain a resin formulation for coating on substrates. 4.The process of claim 1 or 2 wherein the renewable resource has an activehydrogen atom.
 5. A process as claimed in claim 4 wherein the renewableresource is selected from the group consisting of cardanol, saturatedcardanol and urishiol.
 6. The process of claim 1 or 2 wherein therenewable resource is a derivative of cardanol having R₁ as C₁₅H₂₉,C₁₅H₃₁ or any alkyl of 1 to 36 carbon atoms, R₂ as H or alkyl of 1 to 36carbon atoms and R₃ as alkyl of 1 to 36 carbon atoms; aliphatic,aromatic or cycloaliphatic in structure IV.
 7. The process of claim 1 or2 wherein the diisocyanate has R₄ as alkyl of 1 to 36 carbon atoms withaliphatic, aromatic or cycloaliphatic, in structure I.
 8. The process ofclaim 7 wherein the aromatic diisocyanate is selected from the groupconsisting of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,diphenylmethanediisocyanate, p-phenylene diisocyanate, polymethylenepolyphenyl polyisocyanates or any polymeric derivatives ofdiphenylmethanediisocyanate.
 9. The process of claim 7 wherein thealiphatic or cycloaliphatic diisocyanate is selected from the groupconsisting of hexamethylene diisocyanate,2,2,4trimethylhexane-1,6-diisocyanate,2,4,4-trimethylhexane-1,6-diisocyanate, isophoronediisocyanate,1,4-cyclohexane diisocyanate, dicyclohexyl methane-4,4′-diisocyanate, anadduct of 1 molecule of 1,4-butane diol and 2 molecules of isophoronediisocyanate and an adduct of 1 molecule of 1,4-butane diol and 2molecules of hexamethylene diisocyanate.
 10. The process of claim 1 or 2wherein the hydroxyl terminated acrylate has R₅ as alkyl of 1 to 36carbon atoms; or (CH₂CH₂O)_(n), and R₆ as hydrogen or alkyl of 1 to 36carbon atoms in structure II.
 11. The process of claim 10 wherein thehydroxy acrylate is selected from the group consisting of hydroxyethylmethacrylate, hydroxyethyl acrylate, 4-hydroxybutyl acrylate,4-hydroxybutyl methacrylate, 2-hydroxypropyl acrylate, 3-hydroxypropylmethacrylate, hydroxyhexyl acrylate, poly(ethylene glycol) acrylate,poly(ethylene glycol) methacrylate and 12-hydroxydodecanyl acrylate. 12.The process of claim 1 or 2 wherein the isocyanate-hydroxyl couplingreaction is carried out at a temperature in the range of 0-100° C. 13.The process of claim 1 or 2 wherein the isocyanate-hydroxyl couplingreaction is carried out either without solvent (bulk), or in thepresence of solvent selected from the group consisting of dimethylformamide, tetrahydrofuran and dimethyl acetamide.
 14. The process ofclaim 1 or 2 wherein the catalyst used for the isocyanate-hydroxylcoupling reaction is an organometallic catalyst having concentration inthe range of 0.001-0.5 parts per 100 parts of active hydrogen-containingcompound.
 15. The process of claim 14 wherein the organometalliccatalyst is an organotin catalyst.
 16. The process of claim 15 whereinthe organotin catalyst used is selected from the group consisting ofdibutyl tin dilaurate, dibutyltin diacetate, dibutyltin maleate ordioctyltin diacetate.
 17. The process of claim 1 or 2 wherein thephotoinitiator used is an aromatic carbonyl compound.
 18. The process ofclaim 17 wherein the photoinitiator used is selected from the groupconsisting of benzil, benzil dimethyl ketal, acetophenone, substitutedacetophenones, thioxanthone and chlorothioxanthone.
 19. The process ofclaim 3 wherein monofunctional oligomers selected from the groupconsisting of methyl acrylate, methyl methacrylate, ethyl acrylate,ethyl methacrylate and butyl acrylate are formulated.
 20. The process ofclaim 3 wherein multifunctional oligomers selected from the groupconsisting of acrylic esters of aliphatic diols and/or polyols, ethylenediacrylate, trimethylol propane triacrylate and pentaerythritoltetraacrylate are formulated.
 21. The process of claim 3 wherein theradiation source used is a high, medium or low-pressure mercury or xenonlamp.
 22. The process of claim 1 or 2 wherein the curing of theprepolymer results in transparent pealable films.